Property, plant and equipment - Depreciation expense (Detail) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 4,652	$ 4,218
Insurance and Other [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	1,158	1,127
Railroad, Utilities and Energy [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 3,494	$ 3,091